A disk harrow, that is a harrow whose operative tools are disks rather than tines or forks, is often preferred when stumps, roots, or other underground obstructions are likely to be encountered. The disks of such a device must be urged with considerable force down against the ground, but at the same time must be able to move upwardly and out of the way without being damaged should they hit an obstruction. Obviously these functions are somewhat mutually contradictory, so one must normally trade off ability to move out of the way against downwardly effective biasing force.
The best of such agricultural apparatuses normally has several problems. Frequently when one disk is deflected by an obstruction the other disks also respond somewhat, lifting them out of the ground also. In addition these machines are often quite large and cumbersome, making it difficult to use them in orchards or other areas where tight maneuvering might be necessary.